1. Technical Field of the Invention
The present invention relates to a gas turbine engine, in which a compressor impeller is connected to a turbine impeller via a connection shaft, or a compressor and a turbine casing are adjacent to each other or connected to each other.
2. Description of the Related Art
The basic cycle of a gas turbine is the Brayton cycle, and the thermal efficiency thereof changes with an increase in pressure ratio and temperature ratio. For this reason, it is very important to prevent the heat generated at a high-temperature part (combustor) from being transmitted to a low-temperature part (compressor) in view of insuring the cycle performance. It becomes of particular importance in the case the gas turbine engine is downsized. The reason is that it is necessary to achieve a temperature difference between the high-temperature part and the low-temperature part which is similar to a large-sized machine, at shorter distance.
Also, in the case where the gas turbine is used to drive an electric generator, the heat insulation between the high-temperature part of the gas turbine and the electric generator is important. The reason is that, in a permanent magnet of the electric generator, the maximum allowable temperature to function as a magnet according to the Curie point is limited to a low level.
For example, a conventional heat isolation means for reducing an amount of heat conduction from the high-temperature to the low-temperature is disclosed in Patent Documents 1 and 2.
As shown in FIG. 1, a start-up combustor disclosed in Patent Document 1 includes a heat isolation plate 53 engaged on a gas passage in an inside of a casing 51 and having a cooling fluid passage 52, and a heat-retaining layer 54 of a constant thickness provided between the heat isolation plate 53 and an inner surface of the case and filled with an insulation filling therein, to suppress heat input of radiant heat to the casing 51.
As shown in FIG. 2, the heat isolation panel (front heat isolation panel) 60 disclosed in Patent Document 2 includes a high-temperature side part and a low-temperature side part which can be utilized in a combustor for a gas turbine engine, and the low-temperature side part is provided with at least one independent cooling chamber 66. Each cooling chamber 66 is provided with a plurality of film cooling bores 62, through which a refrigerant such as air flows from the low-temperature side part to the high-temperature side part.    Patent Document 1: Japanese Unexamined Patent Application Publication No. H9-33035    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-292362
In the case where the compressor impeller compressing the air is directly connected to the turbine impeller rotated by the hot gas via a connection shaft, there is a problem that since a lot of heat is conducted from the hot turbine impeller to the compressor impeller via the connection shaft, the air in the compressor is heated, and thus the performance of the compressor is deteriorated.
Also, in the case where the combustor for burning the fuel in the pressurized air compressed by the compressor is detached from the compressor and then is installed to a rear side (opposite to the compressor) of the turbine, since the combustion gas generated by the combustor is high temperature, for example, 1000° C. or more, the hot gas is introduced into the turbine. Therefore, the combustor and the turbine are hot, so that a lot of heat is conducted to from the high-temperature part to the compressor side.
In particular, in the case where the compressor and the turbine casing are adjacent to each other or connected to each other in order to downsize the gas turbine engine, the amount of heat conductivity is increased, and the performance of the compressor and the performance of the gas turbine may be deteriorated.
In case of combining and miniaturizing the gas turbine engine and the electric generator, it is preferable that the electric generator is interposed between the compressor and the turbine. In this instance, however, since, in the permanent magnet of the electric generator, the maximum allowable temperature working as a magnet according to the Curie point is low (e.g., 100° C.), it is necessary to further improve the performance of heat insulation thereof.